Carbon content of coal

Pines, A., Aromatic Carbon Contents of Coals, SRCs, and Residues Were Determined by CP-l C-NMR", Under a Subcontract to EPRI, RP-410-1. 

Figure 7 shows several curves which have been proposed to relate carbon content of coals to the a-axis crystallite size (4, 5, 11, 19, 24). Curves I and II are based on criteria now superseded and are considered to be obsolete. From these data, layer diameters between 8 and 9 A. are suggested for the anthraxolite (94% C). Since these values are close to the c-axis lengths (which as reported above may be too large), it is felt that typical crystallites of the anthraxolite may be nearly equidimensional cylinders. 

Figure 12. Relations of specific gravity and carbon content of coals to carbonization temperature. After MacFarlane (24). Dashed lines give parameters of Martinsburg anthraxolite...

Figure I. Relation between the C-methyl content (Kuhn-Roth method) and the alicyclic carbon content of coal values from Kaiser et al. (14) ...

Figure 4. Correlation of reflectance of vitrinite and carbon content of coals (6)...

Coal also contains inorganic components— mineral matter (Chapter 7)— which are determined as mineral ash (Chapter 8). The mineral matter includes minerals such as pyrite (FeS2) and the related mineral marcasite (FeSj), as well as other minerals formed from metals that accumulated in the living tissues of the ancient plants. Quartz, clay, and other minerals are also added to coal deposits by wind and groundwater. The mineral matter lowers the fixed carbon content of coal, decreasing its heating value (Chapter 8). 

Analyses of coals varying in rank have shown that rather surprising correlations exist between the carbon content of coal and the content of various functional groups (Schafer, 1970 Cronauer and Ruberto, 1977) and there appears to be a relationship between functionality and carbon content of coal (Figures 10.15 through 10.19) (Whitehurst et al., 1980). 

Coal composition varies considerably. Approximate carbon content of coal ( hard ) anthracite 70 to 98%, ( soft ) bituminous 40 to 80%, lignite 30 to 40%. 

Fuel switch. The choice of fuel used in furnaces and steam boilers has a major effect on the gaseous utility waste from products of combustion. For example, a switch from coal to natural gas in a steam boiler can lead to a reduction in carbon dioxide emissions of typically 40 percent for the same heat released. This results from the lower carbon content of natural gas. In addition, it is likely that a switch from coal to natural gas also will lead to a considerable reduction in both SO, and NO, emissions, as we shall discuss later. 

Fuel switch. Fuel switch from, say, coal to natural gas reduces the CO2 emissions for the same heat release because of the lower carbon content of natural gas. 

The chemical characteristics of biomass vary over a broad range because of the many different types of species. Table 8 compares the typical analyses and energy contents of land- and water-based biomass, ie, wood, grass, kelp, and water hyacinth, and waste biomass, ie, manure, urban refuse, and primary sewage sludge, with those of cellulose, peat, and bituminous coal. Pure cellulose, a representative primary photosynthetic product, has a carbon content of... 

The carbon content of DRI depends primarily on the direct reduction process used and the way the process is operated. Carbon content can be adjusted within limits by operating changes within the DR process. Most steelmakers prefer slightly more carbon than is required to balance the remaining FeO in the DRI. DRI from gas-based processes typically contains 1 to 2.5% carbon, mostly in the form of cementite [12169-32-3] Fe C. DRI containing approximately 6 to 7% carbon in the form of cementite is called iron carbide. DRI from coal-based, rotary-kiln processes contains very low (ca 0.5%) levels of carbon. 

Coal ash is derived from the mineral content of coal upon combustion or utilization. The minerals are present as discrete particles, cavity fillings, and aggregates of sulfides, sulfates, chlorides, carbonates, hydrates, and/or oxides. The key ash-forming elements and compounds are (4,5) ... 

The main stages of coal combustion have different characteristic times in fluidized beds than in pulverized coal combustion. Approximate times are a few seconds for coal devolatilization, a few minutes for char burnout, several minutes for the calcination of limestone, and a few hours for the reaction of the calcined limestone with SO2. Hence, the carbon content of the bed is very low (up to 1% by weight) and the bed is 90% CaO in various stages of reaction to CaSO. About 10% of the bed s weight is made up of coal ash (91). This distribution of 90/10 limestone/coal ash is not a fixed ratio and is dependent on the ash content of the coal and its sulfur content. 

Solid fuels, unlike gases and liquids, are entirely characterized by their composition. For example, coal can be characterized by its carbon, hydrogen, oxygen, sulfur, and nitrogen content. The water and mineral content of coal are also important means of differentiating coals from various sources. 

One of the most studied of the polyaromatic hydro-carbone (PAH) is benzo(a)pyrene (BaP), which is present in coal tar at coke oven plants. The BaP content of coal tar is between 0.1% and 1 % and it contributes to the serious potential health effects on employees exposed to coke oven emissions. The largest sources of BaP are open burning and home heating with wood and coal. The latter alone contributes 40 percent of all the BaP released each year in the USA. 

For a given energy consumption, fuel change is the only way to reduce C02 and SO emissions at source. Fuel switch from, say, coal to natural gas reduces the C02 emissions for the same heat release because of the lower carbon content of natural gas. Fuel change can also be useful for reducing NO, emissions. Once emissions have been minimized at source, then treatment can be considered to solve any residual problems. 

Moreover, in coals of a similar carbon level, such as Miike coal, Newdell coal, and Grose valley coal, the reactivity of coal decreases greatly with the increasing inert content of coal. 

These reactions proceed smoothly in the presence of hydrogen donating aromatic solvent (1-4) at temperatures from 400°C to 450°C, resulting in the formation of so called solvent refined coal with carbon content of 86-88% on maf basis independent of coalification grade of feed coal. 

H/C = atomic hydrogen-to-carbon ratio V = vitrinite content of coal VM volatile matter St = total sulfur TRM = total reactive macerals The adequacies of these reactivity correlations, expressed as a percentage of the total variation in the data set explained by the model, were 80.0%, 79.2%, and 47.5% respectively. A later paper in the series (21) concentrated on the development of reactivity correlations for a set of 26 high volatile bituminous coals with high sulfur contents, and extended the models previously developed in include analyses of the liquefaction products and coal structural features. These structural features included the usual... 

Just as with organic combustion aerosols, the chemical and physical nature of inorganic solid substrates can have a dramatic impact on the photoreactivity of adsorbed PAH. In 1980, Korfmacher and co-workers reported that BaP, pyrene, and anthracene all pho-tolyzed efficiently in liquid solution but were resistant to photodegradation when adsorbed on coal fly ash. Subsequent studies confirmed this observation and revealed that the carbon content of the ash (and the associated darkening of color) is a key factor in establishing the photostability of these PAHs. Indeed, they were stabilized at relatively small percentages of carbon, e.g., 5% or less (Behymer and Hites, 1985, 1988 Yokley et al., 1986 Dunstan et al., 1989 Miller et al., 1990). 

Production. Silicon is typically produced in a three-electrode, a-c submerged electric arc furnace by the carbothermic reduction of silicon dioxide (quartz) with carbonaceous reducing agents. The reductants consist of a mixture of coal (qv), charcoal, petroleum coke, and wood chips. Petroleum coke, if used, accounts for less than 10% of the total carbon requirements. Low ash bituminous coal, having a fixed carbon content of 55—70% and ash content of <4%, provides a majority of the required carbon. Typical carbon contribution is 65%. Charcoal, as a reductant, is highly reactive and varies in fixed carbon from 70—92%. Wood chips are added to the reductant mix to increase the raw material mix porosity, which improves the SiO (g) to solid carbon reaction. Silica is added to the furnace in the form of quartz, quartzite, or gravel. The key quartz requirements are friability and thermal stability. Depending on the desired silicon quality, the total oxide impurities in quartz may vary from 0.5—1%. 

---